1. Field of the Invention
This invention relates to interior rearview mirror assemblies mounted to a button on the interior of a vehicle windshield.
2. Scope of the Prior Art
Interior windshield-mounted rearview mirrors are commonly used in nearly all vehicles manufactured and sold throughout the world. Different mounts have been designed for different vehicles and are subjected to varying regulations of the different countries in which automobiles and similar vehicles are manufactured.
In the United States and Canada, for example, supports for conventional windshield-mounted rearview mirrors typically include a base member, known commonly as a "button", adhered to the inside of the windshield surface. The button has vertically disposed edges forming rails. The rails may be formed by a bevel on a each edge. A support member, known in the industry as a "channel mount" is slidably fitted over the button whereby sides of the channel mount engage the rails of the button. The channel mount usually includes a mounting means such as an arm, ball joint, or other structure for suspending a rearview mirror in the vehicle compartment for use by the driver of the vehicle. A typical mounting assembly in U.S. vehicles includes a linkage with a double ball joint for adjusting the mirror relative to the windshield in a variety of positions.
Typically, the channel mount is retained on the button by the use of a set screw. However, the use of such a set screw has created numerous manufacturing and maintenance problems in the vehicle assembly. For example, set screws are typically purchased as low-priced commodity items with low tolerances in the screw threads. The inconsistency in such threads can result in cross threading of the screw in its aperture. Sometimes, automatic screwdrivers stop prematurely at a preset stall torque even though the support is not firmly tightened against the button. Sometimes the screws fit so sloppily that there is no torque. Also, the set screw is often stripped out by over-tightening because of the improper sizing of the socket to the set screw or a weakness in the threads of the screw itself.
Attempts have been made in the past to design interior mirror mounts without the use of a set screw. An example may be found in U.S. Pat. No. 4,936,533 issued to Adams et al. on Jun. 26, 1990. This patent discloses a vehicle accessory mounting assembly comprising a spring retainer on the channel mount which is adapted to engage and grip an opposing, raised rib on the surface of the button. The Adams et al. design, however, presents some problems in that it requires a specially designed button and it is virtually impossible to disassemble without utilizing a special tool.
Various governmental agencies have imposed certain standards, test procedures, test conditions, records and recording formats on the manufacture of internal rearview mirror assemblies. The current federal safety standard in the United States is applicable to passenger cars, multipurpose passenger vehicles, trucks, and buses. The stated purpose of the standard is to reduce the number of deaths and injuries that occur when the driver of a motor vehicle does not have a clear and reasonably unobstructed view to the rear. It requires that each passenger car have an inside rearview mirror of unit magnification and that the mirror provide a specified view. The mirror mounting is required to provide a stable support for the mirror. Mirror adjustment by tilting in both horizontal and vertical directions must be provided. Further, if the mirror assembly is located in the head impact area, the mounting is required to deflect, collapse, or break away without leaving sharp edges when the reflective surface of the mirror is subjected to a force of 90 pounds in any forward direction which is not more than 45.degree. from the forward longitudinal direction of the vehicle.
The breakaway feature becomes particularly important when one considers the increasing use of passenger-side air bags. When a passenger-side air bag is inflated, it may impact the windshield-mounted rearview mirror, and can cause the mirror to deflect with a force sufficient enough to break the mirror mount or crack the windshield. In either case, sharp edges resulting from the fractures may be sufficient to prematurely deflate the air bag, thus rendering it ineffective. Proposed future standards may require a windshield-mounted mirror to break away from the mounting without leaving sharp edges at a force substantially less than 90 pounds.
The U.S. Patent to Aikens et al., 4,254,931, (issued Mar. 10, 1981) discloses an interior rearview mirror mount wherein a spring clip on a mounting member slides over a button on a windshield to provide a breakaway mount. The button has a plurality of serrations in an inner face thereof. The spring clip has a lock spring which engages the serrations to prevent easy sliding of the mounting member from the button. The Aikens et al. mount requires a special button which differs from buttons now in use. Further, the plurality of serrations may give a false impression as to whether the mount is fully seated on the button.
The European Economic Community (EEC) currently has motor vehicle regulations which require that a rearview mirror assembly be able to withstand a predetermined static load including the support of a weight without breaking or, if the assembly does break, without glass fragments being released. Consequently, breakaway mirror mounts have been used in Europe for a long time. Most European mirror mounts include a single ball-joint connection with the rearview mirror. An example of such a rearview mirror mount is manufactured by Hohe KG and comprises a specially designed button which is adapted to receive a complementary-shaped channel mount with a spring retainer. Rather than being slidably mounted on the button, however, the channel mount is positioned over the button and then rotated anywhere from 60.degree. to 90.degree. to lock the mount to the windshield button. The button has a detent which is adapted to receive a tab on the channel mount when the channel mount is rotated to the locked position. It has been found that this awkward movement increases the time for installation during assembly of the vehicle.
One of the difficulties encountered with various breakaway designs for interior rearview mirror mounts is in minimizing vibration of the mirror during vehicle travel. Unless the mirror mount is tightly held to the button on the windshield, the mirror will be subjected to vibration which blurs images in the mirror. Thus, mirror mounts must be sufficiently rigid to withstand normal loads imposed during use. In addition, mounts must maintain proper operating characteristics throughout the full range of temperatures which might be experienced.
A need exists for an interior rearview mirror mount which is capable of retaining a mirror element in a stable position, is configured to be usable in the majority of vehicles which have varying windshield areas, angles of inclination, and radii of curvature, which will readily break away from the button when subjected to an impact of predetermined magnitude, which is nevertheless readily removable for replacement, and which is aesthetically pleasing and capable of high-volume production at reduced manufacturing cost from that heretofore experienced.